1. Field of the Invention
This invention relates to reprocessable thermoplastic graft copolymers of propylene polymer and ethylene copolymer. These graft copolymers are prepared by heating propylene polymer and ethylene copolymer in the presence of select peroxides in order to graft the propylene polymer onto the ethylene copolymer.
2. Description of the Prior Art
Polypropylene has excellent high temperature performance compared to polyethylene. However, polypropylene is brittle, rigid, has poor low temperature properties and has a very low elongation, which prevents its use in many applications including use as insulation for wire and cable.
Ethylene copolymers possess a good balance of properties including tensile strength, abrasion resistance, stress crack resistance and low temperature properties. Also, its outstanding electrical properties make it suitable for use as insulation for wire and cable. The ethylene copolymers are generally vulcanized (cured) to provide molded or shaped articles with good physical properties. Also, when used in insulation for wire and cable, the ethylene copolymer is cured to provide improved thermal properties. However, the vulcanization or curing step is expensive and time consuming. Additionally, after vulcanization the material cannot be reprocessed.
U.S. Pat. No. 3,433,573 describes blends of 5 to 95 percent by weight of propylene polymer and 95 to 5 percent by weight of a copolymer of ethylene and a polar monomer such as vinyl acetate. It is stated therein that these compositions have improved flexibility and toughness at both room temperature and below 0.degree. C. while retaining a large measure of its high temperature properties. These compositions may be vulcanized or cured by peroxides or other means.
However, blends of polypropylene and ethylene copolymers are generally incompatible over a wide range which results in unacceptable properties such as, tensile strength, elongation and deformation of a composition containing said blend.